Centerless grinders are widely used in the machine tool industry in the manufacture of cylindrical industrial products, such as fuel injector pins, gears, shafts, and the like. Such grinders are typically utilized to provide a smooth finish or precise dimensions to such cylindrical parts. The workpiece being ground is rotated in a direction counter to that of the grinding wheel while being ground to achieve a uniform finish without excessive heat generation.
Centerless grinders generally contain certain key elements to accomplish such function. These grinders typically have a grinding wheel and a regulating wheel adjacent to and facing each other in a predefined grinding area. The regulating wheel serves to rotate the part being finished or ground, and the grinding wheel performs the grinding and finishing operation. The regulating wheel contacts the workpiece and rotates it in a direction opposite to that of the grinding wheel, usually at a much slower speed. For example, the grinding wheel may rotate at 3000 r.p.m. whereas the regulating wheel may only rotate at 100 r.p.m. in the opposite direction, depending, of course, on the particular application.
The centerless grinders also generally include a dresser for the grinding wheel and a dresser for the regulating wheel along with their associated control components. The dressers serve to reshape the abrasive surface of the wheels since the surfaces may wear unevenly during the grinding operation. Such uneven wear may result in an undesirable finish or imprecise dimensioning of the workpiece.
In some applications, a single grinding machine may actually perform more than one grinding operation thus requiring more than one grinding speed. For example, a centerless grinder may perform a "rough" grinding cycle, which removes a comparatively large amount of stock from the part, at a particular combination of grinding/regulating wheel speed. The same grinder would then change the relationship between the grinding wheel/regulating wheel speed (by changing either or both wheel speeds) before performing a "finish" grinding operation. A finish operation is typically performed at a higher grinding/regulating wheel speed ratio, which removes less stock than the roughing operation thereby achieving a more uniform surface finish.
Large, constant speed motors are typically used to drive the grinding and regulating wheels. A transmission is provided to couple each wheel to its respective motor while also controlling the speed of the wheel relative to the motor. Such transmissions are complex members containing a plurality of gears, shafts, chains, and sprockets. They are typically equipped with a clutch and operator lever to manually shift the transmission thereby changing the gear ratio so as to achieve a different output speed.
Prior art centerless grinders rely on the use of such transmissions as driving means, such as the grinder disclosed in U.S. Pat. No. 4,783,932. This grinder includes a transmission as its driving means such that the drive mechanism is coupled to the regulating wheel so that the drive mechanism and the drive coupling means move jointly with the regulating wheel.
The use of such complex transmission systems on centerless grinders often results in the necessity for frequent repairs. It is not uncommon for the transmission to be rebuilt or replaced several times during the useful life of the centerless grinder. Such repairs are expensive and time-consuming resulting in a reduction in the efficiency of the manufacturing operation since the grinder is unoperational.